Seal coating interior of tubing



Feb. 4 1958 R. I. HAHN SEAL COATING INTERIOR OF TUBING Filed June 25, 1949 /NVENTOR 1144 T 4;, a ATTORNEYS SEAL COATING INTERIOR OF TUBING Application June 25, 1949, Serial No. 101,402

Claims. (Cl. 117-97) This invention relates to the manufacture of welded steel tubing and its object is to provide the interior of the tubing with a permanent sealing coat of non-ferrous metal anchored to the tubing by an alloy bond. This is accomplished by a method which comprises applying to the interior surface of the tubing while it is moving longitudinally a coating of finely divided non-ferrous metal having a melting point lower than steel and dispersed in a spreading liquid, the region of the tubing receiving the coating being at a temperature below the volatilization temperature of the liquid, providing gaseous flux within the tubing, heating the tubing, as it passes, for a time suificient to expel the liquid without concurrently melting the metal powder in order to leave the powder fairly uniformly distributed on the interior surface of the tubing, raising the temperature of the tubing to melt the powder which, in the presence of gaseous flux, spreads to fill pores in the steel and to provide a continuous metal coat, and cooling the tubing to solidify the coat.

The disclosed embodiment of the apparatus for performing the method, provides for applying to the interior surface of the tubing a coating of metal powder dispersed in a spreading liquid at a region of the tubing ahead of the tubing annealer in which the tubing is heated for a time sufficient to expel the spreading liquid and then to a temperature suthcient for annealing purposes and to melt the metal powder which spreads to fill pores of the steel and to provide, on solidifying, a permanent coat.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Figs. 1 and 2 together provide a diagram of a tube mill equipped with apparatus for practicing the present method.

Fig. 3 is a fragmentary, sectional view on a larger scale than Fig. 1 and is taken on the line 3-3 of Fig. 1.

Fig. 4 is a fragmentary, sectional view on the line 44 of Fig. 2.

Referring to Figs. 1 and 2, the mill comprises a tube former which includes a plurality of pairs of rolls 11 which progressively form a flat steel strip S into a tube T with the edges of the strip abutting at the top. The tubing passes between a pair of insulated electrode rolls represented by circle 12 which causes the welding current to pass across the butt joint while the tubing is pressed against the electrodes by a roller 13 supported by a lever 14- pivoted at 15 on a bracket 16 and urged upwardly by metal bellows 17 into which compressed air is introduced by pipe 18.

The tubing passes next under jets of water 19 issuing from the nozzle 2i) and dripping into a funnel 21 connected with drain pipe 22. The tubing then passes between pairs of rolls 24 of a tubing sizer 25. Thetubing then passes successively between pairs of copperrolls ttes atent ice 26, 27 and 28 of an annealer 30. These rolls are housed in cases 29 and connected by refractory tubes 31. Each of the lower'rolls 26, 27 and 28 is attached to a rotatably supported copper shaft 32 (Fig. 4) carrying a copper drum 33 partially submerged in mercury 34 in a metal vat 35. The vat 35 for rolls 26 and 28 may be grounded upon a base 36 which is grounded. The vat 35 for roll 27 and the housing 29 are insulated from the base 36 and from the other housing 29 and are electrically connected with the non-grounded terminal 37 of a current source having a grounded terminal 38.

The tubing T passes from the annealer into a cooler 40 comprising a tube 41 through which the tubing passes and surrounded by a water jacket tube 42. While the tubing T is in the annealer 30, it is surrounded by an atmosphere of non-oxidizing gas introduced through one or more pipes 39.

The mixture of metal powders and a suitable spreading liquid is pumped by a pump 50 through a valve 51 into a closed tank 52, the cover of which supports an electric motor 53 driving an agitator 54 for causing the metal powder to be evenly dispersed in the liquid. Valve 51 is adjusted so that the supply of material will balance the demand. The suspension mixture is forced from the tank 52 by introducing non-oxidizing gas under pressure through a pipe 55 controlled by a valve 56. The suspension mixture flows from the tank into pipe 57 through a flow controlling valve 58 and a pipe 59 which ends in a nozzle 60 located within that portion of the tubing which is under the water jets 19 so that the temperature of the tubing at that region is substantially below volatilization temperature of the liquid. Pipe 59 extends within a pipe 61 through which reducing gas flows under a pressure controlled by valve 62. As shown in Fig. 3, the pipes 59 and 61 enter the tubing T before the edges of the strips are formed in abutting relation.

The dispersion of metal powder in spreading liquid issuing from the nozzle 60 causes the interior surface of the tubing to be coated with a film in which the metal powder is fairly evenly distributed. The gas which enters the tubing from the pipe 61 is preferably 20% to 25% reducing in effect, thereby providing a gaseous flux. Before the tubing reaches rolls 27, it is heated to a temperature sufficient to volatilize the spreading liquid without concurrently melting the metal powder. At or beyond rolls 27, the temperature of the tubing is raised sufficiently to melt the metal powder. In the presence of the gaseous flux, melted metal particles spread out to fill minute pores of the interior surface of the tubing and to provide, when cooled, a continuous coating of substantially uniform thickness anchored to the steel by virtue of having entered the pores. If the powder is of metal capable of alloying with steel, such as copper, tin, bronze, the anchor will be also an alloy bond.

Steel tubing thus coated can be used to convey liquids corrosive to steel but not corrosive to the coating. It can be used to confine gases under pressure, such as refrigerating Freon gas, which otherwise would leak through the tubing in a relatively short time.

The annealer 30 serves not only to anneal the tubing but also to dry the coating of metal powder and then to melt it in order to cause it to spread to provide a permanent corrosion resisting and gas retaining coating. Instead of having the pipe 59 terminate in the spraying nozzle 60, it may be connected to a perforated tube from which brush bristles extend to the inner surface of the tubing. As the tubing moves the bristles spread the coating material on the interior of the tubing. Instead of having separate pipes for conducting gas and coating material, there may be one pipe within the tubing conducting both gas and coating material and the gas which is under pressure may be used to effect rotation of a whirling nozzle which would spread the coating material on the interior of the tubing. By using as a dispersion medium a liquid which, on being heated by the tubing, while in the annealer, will supply a suitable gaseous hurt, it will not be necessary to supply the reducing gas from an outside source. If the metal powder for the coating is such that it does not melt while the tubing is welded, it may be mixed with suflicient spreading liquid to form a paint which is applied to the upper surface of the steel strip before the strip is completely formed into a tube.

When seal-coating is to be carried on concurrently with annealing, the powder should be of metal having a melting point in the range of annealing temperatures. The metal may be copper, bronze or tin.

When using copper powder as a coating material, the copper should be of 60 mesh fineness or finer. The finer the copper, the better the coating operation. About 8 to 10 pounds of copper powder are mixed with 1 /2 gallons of liquid which, for example, can be lubricating oil known as S. A. E. 10. Considerable latitude in the proportions of copper powder and oil is permitted. If there is too much copper powder, the dispersion liquid will be too thick and the coating on the tubing will be bumpy. If there is too little copper powder, the coating will be too thin and will be non-uniform. The proportions given in the foregoing example have been found satisfactory.

f copper powder is used to provide the coat, as the tubing passes between rolls 26 and 27, the temperature of the tubing is raised to about 1800 F., thus volatilizing the dispersing liquid without melting the copper powder, thus leaving the copper powder fairly uniformly distributed upon the interior of the tubing. Between the rolls 27 and 28, the temperature of the tubing is increased to about 2000 F. The tubing is annealed and the copper powder melts and, in the presence of gaseous flux, spreads substantially uniformly over the interior of the tubing and penetrates into the pores thereof and to alloy with the steel.

The gas which protects the interior and exterior of the tubing is preferably 20% to 25% reducing. The gas may have, for example, the following analysis; 10% carbon monoxide, 18% hydrogen, l /2% to carbon dioxide, 1% methane and the balance nitrogen. If it is desired to increase the time period during which the material is molten while on the surface of the tubing, the temperature which the tubing attains at rolls 27 should be above the melting point of the material. If the material is copper, the temperature should be 2000 F. for example. The spacing of rolls 26 and 27 is adjusted to attain the required temperature at rolls 27 and the spacing of rolls 27 and 23 is adjusted to maintain that temperature. The tubing will be properly annealed so long as its temperature between rolls 27 and 28 is above 1600" F.

If the apparatus were used only for coating, and not for annealing, the powders of low melting point metals, such as aluminum or lead-tin alloy, can be used. If lead-tin alloy powder is used, the dispersing liquid can be dilute solution of fiuxing acid. In this case, less heat is required. The heating between rolls 26 and 27 is that required to dry the coating but not to melt the powder. The heating between rolls 27 and 28 is that required to melt the powder.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. The method of coating the interior of steel tubing with a corrosion-resistant coating during the formation of said tubing from substantially flat steel strip by a continuous process of bending and welding and while said tubing is being moved continuously and longitudinally, said method comprising the steps of, introducing into the tube during the movement thereof and at a point where the tube is fully formed, a dispersing liquid containing finely divided particles of a non-ferrous metal having a melting point lower than that of steel, cooling the tubing adjacent the point of introduction of said liquid thereinto in order to maintaina temperature at such point which is insufficient to volatilize the liquid, introducing a reducing gas into the tube adjacent the point of introduction of the dispersing liquid so as to maintain a nonoxidizing atmosphere therein, subsequently heating the tube during its continued movement to a degree sufiicient to volatilize all of the dispersing liquid but below the melting point of the coating metal, thereafter heating the tubing during further movement thereof to a degree sufficient to melt said coating metal and cause it to flow into the pores of the steel so as to form a continuous non-corrosive coating on the steel, and finally cooling the tubing sufiiciently to cause the coating metal to solidify.

2. The method of coating the interior of steel tubing with a corrosion-resistant coating during the formation of said tubing from substantially flat steel strip by a continuous process of bending and welding and while said tubing is bent moved continuously and longitudinally, said method comprising the steps of, introducing into the tube during the movement thereof and at a point where the tube is fully formed, a dispersing liquid containing finely divided particles of a non-ferrous metal having a melting point lower than that of steel, cooling the tubing adjacent the point of introduction of said liquid thereinto in order to maintain a temperature at such point which is insufiicient to volatilize the liquid, introducing a reducing gas into the tube adjacent the point of introduction of the dispersing liquid so as to maintain a nonoxidizing atmosphere therein, subsequently heating the tube during its continued movement to a degree sufiicient to volatilize all of the dispersing liquid but below the melting point of the coating metal, thereafter heating the tubing during further movement thereof to a degree suflicient to melt said coating metal and cause it to flow into the pores of the steel so as to form a continuous noncorrosive coating on the steel, while maintaining a nonoxidizing atmosphere within the tubing at the point Where the coating metal is melted, and finally cooling the tubing sufiiciently to cause the coating metal to solidify.

3. The method of coating the interior of steel tubing with a corrosion-resistant coating during the formation of said tubing from substantially flat steel strip by a continuous process of bending and welding and while said tubing is being moved continuously and longitudinally, said method comprising the steps of, introducing into the tube during the movement thereof and at a point where the tube is fully formed, a dispersing liquid containing finely divided particles of a non-ferrous metal having a melting point lower than that of steel and alloyable with the steel, cooling the tubing adjacent the point of introduction of said liquid thereiuto in order to maintain a temperature at such point which is insuflicient to volatilize the liquid, introducing a reducing gas into the tube adjacent the point of introduction of the dispersing liquid so as to maintain a non-oxidizing atmosphere therein, subsequently heating the tube during its continued movement to a degree sufficient to volatilize all of the dispersing liquid but below the melting point of the coating metal, thereafter heating the tubing during further movement thereof to a degree sufficient to melt said coating metal and cause it to flow into the pores of the steel so as to form a continuous non-corrosive coating on the steel, which upon cooling will be secured to the steel with an alloy bond, and finally cooling the tubing sufiiciently to cause the coating metal to solidify.

4. The method of coating the interior of steel tubing with a corrosion-resistant coating during the formation of said tubing from substantially flat steel strip by a continuous process of bending and welding and while said tubing is being moved continuously and longitudinally, said method comprising the steps of, introducingiuto the tube during the movement thereof and at a point where the tube is fully formed, a dispersing liquid containing finely divided particles of a non-ferrous metal having a melting point lower than that of steel, cooling the tubing adjacent the point of introduction of said liquid thereinto in order to maintain a temperature at such point which is insufllcient to volatilize the liquid, subsequently heating the tubing during its continued movement to a degree sufi'lcient to volatilize all of the dispersing liquid but below the melting point of the coating metal, introducing a reducing gas into the tubing before the dispersing liquid is heated to volatilizing temperature to maintain a non-oxidizing atmosphere within the tubing when the dispersing liquid is volatilized, thereafter heating the tubing during further movement thereof to a degree sufficient to melt said coating metal and cause it to flow into the pores of the steel so as to form a non-corrosive coating on the steel, while maintaining a non-oxidizing atmosphere within the tubing at the point where the coating metal is melted, and finally cooling the tubing suificiently to cause the coating metal to solidify.

5. The method of coating the interior of steel tubing with a corrosion-resistant coating during the formation of said tubing from substantially flat steel strip by a continuous process of bending and welding and while said tubing is being moved continuously and longitudinally, said method comprising the steps of, introducing into the tube during the movement thereof and at a point where the tube is fully formed, a dispersing liquid containing finely divided particles of a non-ferrous metal having a melting point lower than that of steel, cooling the tubing adjacent the point of introduction of said liquid thereinto in order to maintain a temperature at such point which is insuflicient to volatilize the liquid, introducing a reducing gas into the tube adjacent the point of introduction of the dispersing liquid so as to maintain a non-oxidizing atmosphere therein, subsequently heating the tube during its continued movement to a degree sufficient to volatilize all of the dispersing liquid but below the melting point of the coating metal, thereafter heating the tubing during further movement thereof to a degree suflicient to effect annealing of the tubing and to melt said coating metal in order to cause it to flow into the pores of the steel and form a continuous non-corrosive coating thereon, maintaining a non-oxidizing atmosphere within the tubing at the point where the last-mentioned step of heating is eifected, and finally cooling the tubing sufiiciently to cause the coating metal to solidify.

References Cited in the file of this patent UNITED STATES PATENTS 1,730,087 Needle et al. Oct. 1, 1929 1,818,008 Ritter et al. Aug. 11, 1931 2,348,495 Peterson May 9, 1944 2,405,515 Hopkins Oct. 1, 1946 

1. THE METHOD OF COATING THE INTERIOR OF STEEL TUBING WITH A CORROSION-RESISTANT COATING DURING THE FORMATION OF SAID TUBING FROM SUBSTANTIALLY FLAT STEEL STRIP BY A CONTINUOUS PROCESS OF BENDING AND WELDING AND WHILE SAID TUBING IS BEING MOVED CONTINUOUSLY AND LONGITUDINALLY, SAID METHOD COMPRISING THE STEPS OF, INTRODUCING INTO THE TUBE DURING THE MOVEMENT THEREOF AND AT A POINT WHERE THE TUBE IS FULLY FORMED, A DISPERSING LIQUID CONTAINING FINELY DIVIDED PARTICLES OF A NON-FERROUS METAL HAVING A MELTING POINT LOWER THAN THAT OF STEEL, COOLING THE TUBING ADJACENT THE POINT OF INTRODUCTION OF SAID LIQUID THEREINTO IN ORDER TO MAINTAIN A TEMPERATURE AT SUCH POINT WHICH IS INSUFFICIENT TO VOLATILIZE THE LIQUID, INTRODUCING A REDUCING GAS INTO THE TUBE ADJACENT THE POINT OF INTRODUCTION OF THE DISPERSING LIQUID SO AS TO MAINTAIN A NONOXIDIZING ATMOSPHERE THEREIN, SUBSEQUENTLY HEATING THE TUBE DURING ITS CONTINUED MOVEMENT TO A DEGREE SUFFICIENT TO VOLATILIZE ALL OF THE DISPERSING LIQUID BUT BELOW THE MELTING POINT OF THE COATING METAL, THEREAFTER HEATING THE TUBING DURING FURTHER MOVEMENT THEREOF TO A DEGREE SUFFICIENT TO MELT SAID COATING METAL AND CAUSE IT TO FLOW INTO THE PORES OF THE STEEL SO AS TO FORM A CONTINUOUS NON-CORROSIVE COATING ON THE STEEL, AND FINALLY COOLING THE TUBING SUFFICIENTLY TO CAUSE THE COATING METAL TO SOLIDIFY. 